Succinctly stated, the overall objective of the total project is to obtain an understanding of the occurrence, location, binding, variety, changeability and functional role of the "water" present in human dental enamel in relation to various properties of human teeth. The primary enamel samples to be studied are sound enamel obtained from teeth removed from persons near the two extremes of the human life span. The samples will be investigated by a variety of analytic techniques designed (1) to identify unambiguously and to assay the water in dental enamel, (2) to determine the location, state of binding and accessibility of the water in enamel, (3) to explain the irreversibility of the dehydration-hydration cycle of enamel, and (4) to determine if coupled substitutions, involving water, are related to the observed variations in the Ca/P molar ratios and heating-induced reduction of OH deficiencies in enamel. BIBLIOGRAPHIC REFERENCES: Abstracts Published of Presentations at Scientific Meetings "Experiences with X-Ray PFSR: Profiles, LaPO4, and Tooth Enamel", P.E. Mackie, Dennis B. Wiles and R.A. Young, Program and Abstracts, American Crystallographic Association, Series II, 5 42 (1977). "Preliminary Crystal Structure Analysis of Powered Human Tooth Enamel", P.E. Mackie and R.A. Young, J. Dent. Res. 56, (Special Issue), in press (1977).